The Holy verse says:
" And do not weaken in pursuit of the enemy. If you should be suffering - so are they suffering as you are suffering, but you expect from Allah that which they expect not. And Allah is ever Knowing and Wise." (4:104)
I was amazed actually to see that some people consider this verse as a violent verse. I do not see their point of view at all, unless I consider pure and clear evil intention. In the verse God orders Muslims not to weaken when they are in pursuit of their enemy. Have you ever seen a leader telling his troops to pursuit their enemy weakly ..?? God continues that war is a suffering for both Muslims and disbelievers alike. The advantage the Muslims have here is that Muslims expect from God what the disbelievers do not expect from Him namely, the reward which is paradise if they are killed in the war.
God knows human beings and how they think, He is telling them that the road of faith is not paved with flowers, it is a difficult road paved with thorns and sufferings. For this reason the prize is the biggest there is which is paradise.